The present invention relates in general to models employed in restorative or prosthetic dentistry, and more particularly to an indexing pin and locating pin fixed in a removable die of a model and received by a base to which the model is secured.
In the making of a fixed dental prosthesis (i.e. gold and ceramic crown or bridge) it is required that an accurate replica of the existing teeth and gums (dentition) be made. The replicas, herein referred to as models, are made by taking an impression of dentition. Material capable of adapting to the exact shape and dimension of the dentition are, for example, silicon rubber and agar hydrocolloid. The impression is a "negative" model in which plaster, such as calcium sulfatehemihydrate, is poured. Upon removal from the impression, the plaster forms the model on which the prosthesis is constructed. The model is secured to a base of plaster to increase its overall strength.
The plaster model comprises teeth which are replicas of the teeth remaining in the mouth of the patient and a replica of the teeth to be prepared by prosthetic or restorative dentistry. It is the teeth prepared for the prosthesis to be developed upon that employs an indexing and locating pin.
The replica of the teeth to be prepared by prosthetic or restorative dentistry is known as a die. It is desirable in restorative dentistry that the die be removable from and replaceable in the model. Further, the die should be indexed in the model to reposition itself in all planes after removal. The replaced die should not vary or move from its original position in the model in any plane more than .+-.0.001 inch. Also, the die in its vertical removement from the model should be free to move in all planes immediately upon the vertical removal action to provide free play for removal of undercut or eccentric dies. The removal is in a direction perpendicular to the occular plane. Of course, the removal is from the base upon which the model is secured. While disposed in the model, the die should be retained in place as to be unyielding to the normal forces and pressures, for example torsion, that may be applied to it during the fabrication of the prosthesis. Thus, a die must be capable of being indexed in the model, must be removable with facility, and must be stable against forces applied thereto during the fabrication of the prosthesis.
In the patent to Robert A. Samuel et al. U.S. Pat. No. 3,952,415, issued on Apr. 27, 1976, for J-shaped Pin For Making Dental Prosthesis, there is disclosed a pin which is fixed in the die. The pin has a locating leg and an indexing leg interconnected by an arcuate portion of the pin. The legs extend downwardly from the die to be received by the base to which the model is secured.
It has been found that debris, such as plaster chips and dust, collects in the opening which receives the indexing leg. The debris is often generated by a technician cutting or grinding on the die or base. The collection of debris in the opening receiving the indexing leg inhibits or restricts the full insertion or indexing movement of the indexing leg. Such a restriction results in inaccuracies.
In the patent to Bernard Weissman, U.S. Pat. No. 3,153,283, issued on Oct. 2, 1964, for Dowel Pin Assembly For Dental Dies, there is disclosed a dowel comprising a dowel pin and a complementary dowel sleeve. The sleeve provides indexing for the dowel pin that is insertable in and removable from the dowel sleeve. The sleeve defines a bore disposed below and in alignment with the tip of the dowel pin.